Current supply device for ceramic electrodes

ABSTRACT

An electrode assembly used with furnaces for the melting of conductive masses such as glass comprises a ceramic electrode which has an exterior end face abutted by a highly ductile mass which is placed under pressure thereagainst and heated to a temperature closely below its melting point. Because the mass is highly ductile at this temperature and is pressed thereagainst by a ram, the mass closely and intimately conforms to the end face of the ceramic electrode and facilitates the application of current to the electrode. Preferably the ram is spring-biased against the mass and is mounted for angular movement to maintain a centered relationship relative to the electrode.

United States Patent [191 Pieper et a1. 2

1111 3,826,858 [451 July 30, 1974 CURRENT SUPPLY DEVICE FOR CERAMIC ELECTRODES [76] Inventors: Helmut Pieper, Ketteler Str. 1 1, 877

Lohr; Gunther Umlauf, Ringstr. 8, Steinbach am Wald, both of Germany 22 Filed: July 24,1973

21 Appl. No.1 382,150

[30] Foreign Application Priority Data July 25, 1972 Germany 2235703 [52] US. Cl. 13/6 [51] Int. Cl C03b 5/00 [58] Field of Search 13/6; 339/244 R, 252 R [56] References Cited UNITED STATES PATENTS 3,391,236 7/1968 Blumenfcld 13/6 3,681,506 8/1972 Can 13/6 Primary Examiner-Roy N. Envall, Jr. Attorney, Agent, or Firm-Fitch, Even, Tabin & Luedeka [57] ABSTRACT An electrode assembly used with furnaces for the melting of conductive masses such as glass comprises 6 Claims, 1 Drawing Figure CURRENT SUPPLY DEVICE FOR CERAMIC ELECTRODES The present invention relates to a device for transmitting electrical energy to an electrode of ceramic material, preferably of tin oxide.

Electrodes made of ceramic materials are employed for the melting of conductive masses, such as glass, and they offer the advantage of having an extremely low degree of consumption only since such electrodes, in contrast with metallic or graphite-containing electrodes, do not oxidate. However, it has been found to be disadvantageous that the power or current supply to the electrodes which become conductive only at substantial temperatures, can be effected with difficulty only.

It is already known (US. Pat. No. 3,391,237) to provide electrodes of ceramic material with bores and to establish a liquid metallic phase within such bore, whereby a conductor is immersed into such phase for current supply purposes. However, it has been found to be of disadvantage in such electrodes that they tend to rupture or break in continuous operation due to the temperature inhomogeneities occurring within the tin oxide electrode, such that the electrodes are destroyed. Besides, current supply means of this conventional type suffer from the further drawback that in practical operation only vertical electrodes can be equipped with such a current supply means.

Accordingly, it is the object of the present invention to provide a current supply device for ceramic electrodes, particularly tin oxide electrodes, which current supply device, in general, does no longer show the abovementioned drawbacks and the drawbacks of the prior art, which permits the installation of the electrodes both on vertical and in horizontal position, which is of simple construction and intrinsically safe in operation, which permits the glass furnace to be repeatedly started without causing a destruction of the electrodes of ceramic material, which is not affected by the working of the construction material of the furnace, wherein a destruction of the tin oxide electrode is excluded even after a large number of load or stress cycles, and which provides an absolutely uniform temperature and stress gradient especially interiorly of the electrode.

According to the invention, this object is solved in that a metallic mass heated to a point closely below its melting point and being highly ductile at such temperature, is placed as a conductor with pressure contact between said electrode and the current-conducting parts.

Advantageously, the ductile, conductive mass or composition may comprise silver solder, and the electrode may have a smooth head face against which the ductile, conductive mass is'pressed with a constant, adjustable force by means of a ram consisting of a conductive material.

In order to provide a uniform pressure contact of the conductive, ductile mass over the complete head face of the electrode, and in order that the ram will always press against the head face in a direction exactly perpendicular to such face, the ram may react through a spring with a certain degree of angular movability, and the pressure contact surfaces of the ram and of the ceramic electrode may be of slightly conical configuration so as to be self-centering.

In order to take up the force of pressure contact of the conductive, ductile mass, advantageously the ceramic electrode may have an annular shoulder for its support on the refractory material of the furnace wall, and a portion of the electrode may protrude from the furnace wall to such extent that, without extra cooling, a temperature of from about 500 to 600C is produced at the head face, at which temperature the ductile, conductive metallic mass has a sufficiently intimate adherence to the head face of the electrode while it is not yet squeezed out from the gap between the ram and the head face of the electrode under the pressure exerted by the ram.

Below, an exemplary embodiment of the invention is described in greater detail by referring to a drawing wherein the current supply device according to the invention is shown in schematical sectional view in combination with an electrode.

The electrode of ceramic material, preferable tin oxide, is indicated at 1 and it passes through a bore in the I wall 9 of a glass (melting) furnace or a similar melting furnace. The electrode extends with its right hand end, as shown in the Figure, into the molten material in order to apply the electrical current to such molten material.

The other end of the electrode at the left-hand side as shown in the Figure extends out from the furnace wall 9 which consists of a refractory material. At its end remote from the molten material, the electrode has an annular shoulder which reacts against the refractory material and thereby allows a contact pressure to be applied to the electrode which, besides, is inserted into the bore of the refractory material 9 with a clearance fit.

The current supply device proper is attached to supports 10 of the brickwork of the furnace; it comprises a hollow cylinder 6 the position of which relative to the support 10 may be adjusted by means of a screw 11, and a piston or ram 3 which, through a piston rod 4, is connected to a ceramic body 5 guided within said cylinder 6 with substantial clearance. The ceramic body 5 is supported against the bottom face of the cylinder 6 via a helical compression spring 7.

The piston 3 is provided with an annular, axially projecting rim, and between its front face directed towards the electrode and the head face of the electrode 1 there is inserted an intermediate layer of a metallic, ductile material which may be pressed by the ram 3 against the head face of the electrode 1 in such a manner that a uniformly low electrical resistance exists at any place in the transition between the electrode 1, the ductile metallic mass 2 as the intermediate layer and the ram 3.

The electrical energy per se is applied to the ram 3 through conductor 8, and this energy flows into the ceramic electrode 1 in an absolutely uniform manner, so that the electrode, likewise, has the electrical current flowing therein in an absolutely uniform manner, whereby a uniform temperature drop or gradient from the molten material to the head face is provided within the electrode.

By means of such uniform temperature gradient, in homogeneities of temperature interiorly of the electrode are prevented from occuring, whereby it is avoided that temperature stresses which would destroy the electrode are produced within the electrode body.

Obviously, in the case of a point-like application of the power supply, the electrode which has a substantial natural resistance in the range of lower temperatures, would be subjected to particularly high heating at such point so that substantial and non-uniform temperature stresses would result.

Now, the length of the portion of the electrode protruding out from the furnace wall 9 is selected such that the transition layer 2 is just at a temperature of from about 500 to 600C which is favorable for such layer and at which this layer is sufficiently ductile, but not yet so soft that it could be squeezed out from the gap between the ram 3 and the electrode 1.

If different temperatures exist at the end of the electrode, apparently other intermediate layers 2 could be employed, provided they are sufficiently ductile, stable and conductive at the respectively existing temperature. In this connection, other intermediate layers than such of metallic materials only could be used, too.

According to the invention, silver solder having a melting point between 779 and 840C (Degussa alloy 835) is used for the intermediate layer 2, which silver solder provides the desired properties at a temperature of about 500 to 600C.

Further, according to the invention, the head face of the electrode 1 and the front face of the ram 3 may be of slightly conical shape such that the ram during its pressure contact is always centered relative to the electrode and the connection 4 is always in an axial-parallel position relative to the electrode 1.

In this connection, it is essential to the invention that the ceramic block 5 is movable within the cylinder 6 such that the exact positioning of the ram 3 relative to the electrode 1 is not impeded in spite of the pressure exerted by the spring 7.

In particular, any variation in the position between the electrode and the supports 10 during the starting and shut-off of the furnace may be compensated for in this manner.

Then, the cylinder may be moved towards the electrode l by means of the screw 11 and the requisite contact pressure may be adjusted thereby, such that, on the one hand, a good electrical connection from the intermediate layer 2 to the electrode I exist, while, on the other hand and as explained above, the intermediate layer 2 is not squeezed out from the gap between the ram 3 and the electrode 1.

With the use of the ceramic body 5, it is ensured that the electrode and the current supply 8 to the electrode are both electrically and thermally insulated relative to the support frame 10, while a power transmission is provided in the desired way by compensating for length and angular variations.

The current supply device according to the invention is based upon the finding that ceramic electrodes can only be employed with success and successfully operated with alternating temperature stresses if an absolutely uniform supply of the current through the head face of the electrode is affected, such that the electrode, thus, has the current flowing in an absolutely uniform manner over its cross-sectional area to thereby be heated in an absolutely uniform manner over its entire cross-sectional area.

What is claimed is:

1. An electrode assembly for use with a furnace in electrical heating of a molten mass comprising a ceramic electrode having one end with an end face for receiving electrical current and having an opposite end for projecting into a furnace, a metallic mass positioned in abutting engagement with said end face of said ceramic electrode and being highly ductile at a temperature closely below its melting point with one side thereof being pressed against said electrode end face for conforming with and having intimate contact with said electrode end face when heated to said temperature and pressed against said end face, pressure applying means including a ram surface pressed against the other side of said metallic mass for pressing said metallic mass into said intimate contact to conform to said ceramic end face when heated, and electrical conductor means electrically connected to said metallic mass for applying electrical current to and through said metallic mass to said electrode and for generating the heat to melt the molten mass and to heat said metallic mass to said temperatureclosely below its melting point.

2. The assembly in accordance with claim 1 in which said mass comprises silver solder and said temperature is within the range of 500 to 600 C.

3. The assembly in accordance with claim 1 in which said end face on said electrode is conically shaped and in which pressure applying means comprises a ram having said ram surface of a complementary shape for self centering relative to said conically shaped end face of said electrode.

4. The assembly in accordance with claim 3 in which said electrode has an enlarged shoulder for engaging surrounding support for said electrode to resist the pressure from said ram.

5. The assembly in accordance with claim 3 in which said pressure applying means further comprises a spring for urging said ram and for allowing angular movement of said ram, and an insulating body for preventing electrical current from flowing from said pressure applying means to a framework supporting the same.

6. In combination with a furnace for electrically heating molten materials, the improvement comprising: a refractory furnace wall having an aperture therethrough between an outer and inner surface thereof, a ceramic electrode inserted into said aperture and projecting therethrough, an external end on said electrode having an enlarged shoulder portion for abutting said outer wall surface, an end face on said external end of said electrode, a metallic mass for abutting said end face of said electrode and for applying electrical current to said electrode, said metallic mass being heated to a temperature closely below its melting point and for being highly ductile at such temperature, a ram having a face engaging the other side of said metallic mass, a spring means pressing said face of said ram against said metallic mass and pressing the latter against said end face of said electrode, said shoulder portion of said electrode engaging said furnace wall and resisting inward pushing of said electrode, and support means for holding said spring means and including an insulating body insulating said support means from receiving electrical current. 

1. An electrode assembly for use with a furnace in electrical heating of a molten mass comprising a ceramic electrode having one end with an end face for receiving electrical current and having an opposite end for projecting into a furnace, a metallic mass positioned in abutting engagement with said end face of said ceramic electrode and being highly ductile at a temperature closely below its melting point with one side thereof being pressed against said electrode end face for conforming with and having intimate contact with said electrode end face when heated to said temperature and pressed against said end face, pressure applying means including a ram surface pressed against the other side of said metallic mass for pressing said metallic mass into said intimate contact to conform to said ceramic end face when heated, and electrical conductor means electrically connected to said metallic mass for applying electrical current to and through said metallic mass to said electrode and for generatiNg the heat to melt the molten mass and to heat said metallic mass to said temperature closely below its melting point.
 2. The assembly in accordance with claim 1 in which said mass comprises silver solder and said temperature is within the range of 500* to 600* C.
 3. The assembly in accordance with claim 1 in which said end face on said electrode is conically shaped and in which pressure applying means comprises a ram having said ram surface of a complementary shape for self centering relative to said conically shaped end face of said electrode.
 4. The assembly in accordance with claim 3 in which said electrode has an enlarged shoulder for engaging surrounding support for said electrode to resist the pressure from said ram.
 5. The assembly in accordance with claim 3 in which said pressure applying means further comprises a spring for urging said ram and for allowing angular movement of said ram, and an insulating body for preventing electrical current from flowing from said pressure applying means to a framework supporting the same.
 6. In combination with a furnace for electrically heating molten materials, the improvement comprising: a refractory furnace wall having an aperture therethrough between an outer and inner surface thereof, a ceramic electrode inserted into said aperture and projecting therethrough, an external end on said electrode having an enlarged shoulder portion for abutting said outer wall surface, an end face on said external end of said electrode, a metallic mass for abutting said end face of said electrode and for applying electrical current to said electrode, said metallic mass being heated to a temperature closely below its melting point and for being highly ductile at such temperature, a ram having a face engaging the other side of said metallic mass, a spring means pressing said face of said ram against said metallic mass and pressing the latter against said end face of said electrode, said shoulder portion of said electrode engaging said furnace wall and resisting inward pushing of said electrode, and support means for holding said spring means and including an insulating body insulating said support means from receiving electrical current. 